In a digital communication system, frequency selectivity and time variability in a transmission line arise because of multipath phasing caused by a transmission signal being reflected by buildings or the like or Doppler variation caused by the terminal moving. In such a multipath environment, a received signal becomes a signal in which a transmission symbol and a symbol arriving after a delay time interfere with each other.
With this kind of transmission line having frequency selectivity, a single carrier block transmission method has recently attracted attention in order to acquire the best receiving characteristics (see, for example, Non Patent Literature 1 listed below). The single carrier (SC) block transmission system can reduce the peak power compared with an OFDM (Orthogonal Frequency Division Multiplexing) transmission method, which is multi-carrier (Multiple Carrier: MC) block transmission (see, for example, Non Patent Literature 2 listed below).
With a transmitter that performs SC block transmission, measures against multipath phasing are taken by performing, for example, the following kinds of transmission. First, after generating a PSK (Phase Shift Keying) signal or a QAM (Quadrature Amplitude Modulation) signal, which are digital modulation signals, in a “Modulator”, the digital modulation signal is converted to a time domain signal by a precoder and an IDFT (Inverse Discrete Fourier Transform) processing unit. Thereafter, as a measure against multipath phasing, a CP (Cyclic Prefix) is inserted by a CP insertion unit. The CP insertion unit copies a predetermined number of samples behind the time domain signal and adds the samples to the head of a transmission signal. In addition to this method, as a measure against multipath phasing, ZP (zero Padding: zero insertion) is performed by inserting zero into a start portion and an end portion of data.
Furthermore, in order to suppress transmission peak power, in a transmitter that performs SC transmission, a precoder normally performs DFT (Discrete Fourier Transform) processing.